The invention relates to an ellipsometer for the examination of a sample.
Ellipsometers are used as optical measuring devices to determine the physical parameters of samples. For this, a light beam is directed onto a sample, enabling the characteristics of the sample to be obtained due to the change in the polarization of the light upon reflection from the sample or the transmission through the sample. In particular, ellipsometry allows very thin film layers and film thicknesses as well as indices of refraction of the samples to be determined. This is particularly important in wafer production for integrated circuits.
Due to the increased integration level of these wafers, it is necessary to evaluate sample characteristics on increasingly smaller measuring surfaces. For this reason, generating a small measuring spot is an important characteristic of ellipsometers.
To obtain the most comprehensive information possible regarding the characteristics of the samples, spectroscopic ellipsometers with polychromatic light sources instead of monochromatic ellipsometers are increasingly used. This method has the disadvantage that with known systems, it is difficult to focus polychromatic light on a small measuring spot.
Ellipsometers that use reflective optics (mirror systems) for focusing are known, in which complex beam paths develop regularly. Furthermore, the use of mirror systems results in a non-centralized (off-axis) beam path that in turn results in geometric errors during imaging.